The present invention relates generally to a warning device and method for a heating system. More particularly, the present invention relates to a method and apparatus for indicating when a compressor for a heat pump system fails.
In known heat pump systems it is customary to provide an auxiliary or supplemental heater, usually an electric resistance heater, which is activated to supplement the heat produced by the heat pump system. It is typical to have the auxiliary heater activated by a second thermostat set at a predetermined number of degrees below the setting of a primary thermostat which activates the heat pump system. However, a device for indicating that the auxiliary heater has been activated is not ordinarly provided. Also, the auxiliary heater may be required to provide substantially all of the heat for a space to be heated in the case of a compressor failure within the heat pump system. In the absence of a warning device, the owner of the system has no reason to suspect any malfunction within the heating system since the temperature within the space to be heated is maintained at a desired temperature.
In view of the rapidly increasing cost of energy, it is desirable to provide a warning device which indicates when the compressor has failed so that proper servicing can be obtained. It is further desirable to provide a warning device which is only actuated during a compressor malfunction or failure. In other words, a warning system should not indicate a malfunction when the auxiliary heater is activated merely as a supplement to the heat pump system due to an extremely low outside air temperature for which the heat pump system is incapable of transferring sufficient heat to the space to be heated.
Warning devices for indicating compressor malfunction or failure within a heat pump system are apparently not known. Warning devices for other systems requiring temperature modulation are known which systems rely upon various temperature differentials. One such arrangement provides a monitor for indicating undesirable conditions within a refrigeration system. The arrangement comprises a pair of thermistors which sense two different temperatures which have a known relationship within the system, for example, the ambient air temperature and the temperature of the refrigerant. A first alarm signal is produced when the difference between these temperatures exceeds a predetermined value, and a second alarm signal is produced when the difference between these two temperatures is less than the predetermined value. A device of this type is disclosed in U.S. Pat. No. 3,707,851 issued Jan. 2, 1973 to McAshan, Jr. It is submitted that a device of this type is not readily adaptable to a heat pump system for indicating compressor failure in the system.
A further proposed device for providing corrective measures in the case of a temperature imbalance within a system comprises a device for preventing overheating of an automobile engine particularly when an air conditioning system is driven by the engine. A controller receives temperature data from two sensors. A first temperature sensor consists of a thermostat mounted in the radiator of the engine which sensor continuously monitors the temperature of the engine coolant. A second temperature sensor is attached to the surface of a conduit leaving a condenser for the air conditioning system. When either or both of the signals exceeds a predetermined maximum value, the controller actuates a pump which sprays water directly onto the condenser to cool the condenser of the air conditioning system. A system of this type is disclosed in U.S. Pat. No. 3,926,000 issued Dec. 6, 1975 to Scofield.
Other warning device systems are disclosed in U.S. Pat. Nos. 2,439,331 issued Apr. 6, 1948 to Bean and 2,617,867 issued Nov. 11, 1952 to Welch. These patents relate generally to devices which produce a warning signal if the temperature in the refrigeration system exceeds a predetermined value or if the electricity to the system is cut off.
It is an object of the present invention to provide a simple and effective warning device for a heating system which indicates an abnormal condition within the heating system.
It is a further object of the present invention to provide a warning device for a heat pump system which is effective to indicate that a compressor in the heat pump system has failed or to indicate that an auxiliary heater has been activated but does not indicate a malfunction when the heat pump system is in a cooling mode.
Still a further object of the present invention is to provide a warning device for a heat pump system which can be readily installed by a home owner on an existing heat pump system without requiring the use of special tools or knowledge.
Still a further object of the present invention is to provide a heat pump warning device which is relatively low in cost and is effective to constantly monitor the operation of the heat pump system.
These objects and many others are achieved by a warning device adapted particularly for use with a heat pump system including an auxiliary heater arranged in an outlet duct for heated air from the system. The warning device includes a first temperature sensor adapted for indicating the temperature of a working fluid for the heat pump system leaving a compressor for the system. A second sensor is adapted for indicating the temperature of heated air in the outlet duct downstream from the auxiliary heater. A third sensor is adapted for indicating the temperature of ambient air in a space to be heated. A comparator is provided for comparing the three sensed temperatures and for activating a signal when the comparator indicates that the heated air temperature is greater than the working fluid temperature which is greater than or equal to the ambient air temperature.
According to a preferred embodiment of the present invention, the comparator comprises a window comparator with an upper limit set by the heated air temperature and a lower limit set by the ambient air temperature. In this way, a signal indicating either activation of the auxiliary heater or a compressor malfunction is activated whenever the working fluid temperature falls within the prescribed window.
A further aspect of the present invention includes an arrangement for preventing activation of the warning signal when the auxiliary heater is activated only to supplement the heat pump system. According to a further feature of the present invention, the warning device is activated separately from the heat pump system whereby the warning signal can remain in the indicating condition for a period of time after deactivation of the heat pump system. Still further according to the preferred embodiment each of the temperature sensors comprises a thermistor the voltage across which varies with a change in temperature. The warning signal may be either audible, visual or both audible and visual.